PHYLUM NEMATHELMINTHE.S 



301 



Between the enteric canal and 

 the body-wall is a distinct space, 

 the body-cavity, containing a 

 clear fluid and more or less en- 

 croached upon by the protoplasmic 

 processes of the muscle-cells. The 

 cavity is bounded externally by 

 these processes, internally by the 

 outer cuticle of the intestine : there 

 is no trace of epithelial lining 

 such as occurs in most of the higher 

 animals The body-cavity of the 

 Nematode, in fact, does not exactly 

 correspond to the coelome to bo 

 met with in most higher phyla. 

 It is not to be derived, directly or 

 indirectly, from the archenteron of 

 the embryo, and it does not lie, 

 like a true coelome, between layers 

 of the mesoderm. 



The excretory system presents 

 a certain resemblance to that of 

 Platyhelminthes. It consists of 

 two longitudinal canals {ex. v.), one 

 in each lateral line. Anteriorly 

 these pass to the ventral surface, 

 unite with one another, and open 

 by the minute excretory pore (ex.p.) 

 already noticed. The system is not 

 ciliated, and contains no flame- 

 cells. Both canals are excavations 

 in a small number of enormously 

 elongated and branched cells, each 

 cell having a single nucleus. 



The nervous system consists 

 of a ring (nv. r.) surrounding the 

 pharynx and giving off six nerves 

 forwards and six backwards (Fig. 

 241). Of the latter two are of 

 considerable size, and run in the 

 dorsal and ventral lines respectively 

 {dln,vln.). They are connected with 

 one another by transverse com- 

 missures (c), and the ventral nei've 

 swells into a ganglion just in 

 front of the anus. The pharyngeal 

 nerve-ring contains nerve-cells, and 



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